176 ANNALS OF THE MISSOURI BOTANICAL GARDEN 



[Vol. 2 



tinue to develop equally, the dicotyledonous condition is at- 

 tained ; if one of the growing points ceases to develop, the con- 

 tinued growth of the whole cotyledonary zone is associated 

 with that of the other growing point, and the monocotyledon- 

 ous condition is attained. In like manner, polycotylcdony is 

 simply the appearance and continued development of more 

 than two growing points on the cotyledonary ring. It fol- 

 lows that cotyledons are always lateral structures, arising 

 from the peripheral zone developed at the top of a more or 

 less massive proembryo. This reduces cotyledony in general 

 to a common basis in origin, the number of cotyledons being 

 a secondary feature. The constancy in the number of coty- 

 ledons in a great group is no more to be wondered at than the 

 same constancy in the number of petals developed by the 

 petaliferous zone. This is a brief statement of the thesis of 

 our previous paper, detached from the evidence upon which 

 it was based. 



It was our purpose to extend the investigation far enough 

 to include all of the representative regions of monocotyledons, 

 so that the conclusion could be tested sufficiently to lead either 

 to its abandonment or to its establishment. This second paper 

 deals with a study of the embryos of grasses, which have been 

 examined more extensively, perhaps, than the embryos of any 

 other monocotyledonous group. As a result of this extensive 

 study there are available many accurate records in the form 

 of good figures, giving the details of embryogeny in such a 

 way that interpretation is almost as satisfactory as it would 

 be from the actual material. Of course this use of illustra- 



tions has been checked by the direct inspection of more or 

 less material. 



The embryo of grasses early attracted special attention be- 

 cause it does not seem to conform to the plan of the ordinary 

 monocotyledonous embryo. Certain structures appear that 

 could not be accounted for, but they enriched terminology. As 

 a consequence, the nature of scutellum, epiblast, and coleoptile 

 became subjects of discussion. It was to be expected that 



